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#1
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![]() "Denny" wrote in message ups.com... Paper material in the bed of my truck at 55mph rotates once or trwice in that standing vortex then vanishes over the tailgate - never to be seen again... Any empty, plastic gas can left against the tailgate slides up against the back of the cab - again that standing vortex... Now, that the gate up has less drag overal still amazes me, in spite of knowing what is theoretically happening... denny I forget which brand truck we were looking at (Ford?), but it had a sculpted shape to the top of the tailgate about 8" wide. The salesman said it helped to improve gas mileage... |
#2
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![]() "Blueskies" wrote I forget which brand truck we were looking at (Ford?), but it had a sculpted shape to the top of the tailgate about 8" wide. The salesman said it helped to improve gas mileage... He was wrong. It is to provide extra clearance for people towing 5th wheel or gooseneck trailers. -- Jim in NC |
#3
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![]() "Morgans" wrote in message ... "Blueskies" wrote I forget which brand truck we were looking at (Ford?), but it had a sculpted shape to the top of the tailgate about 8" wide. The salesman said it helped to improve gas mileage... He was wrong. It is to provide extra clearance for people towing 5th wheel or gooseneck trailers. -- Jim in NC No, it was not a 5th wheel clearance thing. I did not describe it very clearly. Regular rectangular tailgate with a wide upper (top when closed) edge... |
#4
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Blueskies wrote:
"Morgans" wrote in message ... "Blueskies" wrote I forget which brand truck we were looking at (Ford?), but it had a sculpted shape to the top of the tailgate about 8" wide. The salesman said it helped to improve gas mileage... He was wrong. It is to provide extra clearance for people towing 5th wheel or gooseneck trailers. -- Jim in NC No, it was not a 5th wheel clearance thing. I did not describe it very clearly. Regular rectangular tailgate with a wide upper (top when closed) edge... You see it on a lot of trucks. It used to be that a box van was just that, a box. A decade or so ago, they started rounding the front edges of the box. Can you say "fairing". Some started rounding the back corners also. I've seen SUV's with what looks like reverse scoops that could have to catch the air passing over the top of the vehicle and blow it down the back. Counterintuitive until you realize that attached flow offers less drag. The thick tailgate with the rounded edge keeps the air in attached flow longer. Even a small amount, just a few inches, offers major improvements over the previous generations 90 degree chop offs. |
#5
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![]() You see it on a lot of trucks. It used to be that a box van was just that, a box. A decade or so ago, they started rounding the front edges of the box. Can you say "fairing". Some started rounding the back corners also. I've seen SUV's with what looks like reverse scoops that could have to catch the air passing over the top of the vehicle and blow it down the back. Counterintuitive until you realize that attached flow offers less drag. You have been tricked! The attached downward flow has nothing to do with drag; but is to keep exhaust and also road dirt away from the rear of the vehicle. Similar ducts became a standard feature of tull sized station wagons during the '60s and '70s. The thick tailgate with the rounded edge keeps the air in attached flow longer. Even a small amount, just a few inches, offers major improvements over the previous generations 90 degree chop offs. I have yet to examine the rounded tail gate, but have my doubts. Suffice it to say that some salesmen are even more creative than the brochure writers--so you might compare the company litterature to the salesman's assertion. Peter |
#6
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![]() "Ernest Christley" wrote I've seen SUV's with what looks like reverse scoops that could have to catch the air passing over the top of the vehicle and blow it down the back. Counterintuitive until you realize that attached flow offers less drag. That scoop helps drag, but more importantly, it prevents carbon monoxide from entering in the back window when it is open and driving at highway speeds. When a chopped off SUV has the window open, that low pressure area in the back gathers up the exhaust, and the swirling motion of the vortex allows some to enter in though the open window. Not good. The scoop supplies fresh air flowing down from the top, and keeps the bad air down lower than the open window. They have been doing that since the 60's, on old station wagons, before they cared about mileage and aerodynamics. -- Jim in NC |
#7
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You guys haven't mentioned the biggie - roof racks. Removing the cross bars
from my Grand Cherokee added 2MPG. Glider pilots look at roof racks and see open air brakes. I can't believe the number of vehicles I see in Denver with ski racks in July. Then, of course, you can park the truck. I understand that trucks have very low drag when parked. If the vehicle has a MPG computer, you can see what speed does to MPG. At 65, my Jeep gets 19MPG. At 55, it gets 24MPG. At 45, it gets 36MPG. If you do the numbers, saving two minutes by driving fast costs big time. Those are REALLY expensive minutes - more than the rental on some airplanes. Bill Daniels "Morgans" wrote in message ... "Ernest Christley" wrote I've seen SUV's with what looks like reverse scoops that could have to catch the air passing over the top of the vehicle and blow it down the back. Counterintuitive until you realize that attached flow offers less drag. That scoop helps drag, but more importantly, it prevents carbon monoxide from entering in the back window when it is open and driving at highway speeds. When a chopped off SUV has the window open, that low pressure area in the back gathers up the exhaust, and the swirling motion of the vortex allows some to enter in though the open window. Not good. The scoop supplies fresh air flowing down from the top, and keeps the bad air down lower than the open window. They have been doing that since the 60's, on old station wagons, before they cared about mileage and aerodynamics. -- Jim in NC |
#8
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![]()
In article ,
"Bill Daniels" bildan@comcast-dot-net wrote: You guys haven't mentioned the biggie - roof racks. Removing the cross bars from my Grand Cherokee added 2MPG. Glider pilots look at roof racks and see open air brakes. I can't believe the number of vehicles I see in Denver with ski racks in July. Then, of course, you can park the truck. I understand that trucks have very low drag when parked. If the vehicle has a MPG computer, you can see what speed does to MPG. At 65, my Jeep gets 19MPG. At 55, it gets 24MPG. At 45, it gets 36MPG. If you do the numbers, saving two minutes by driving fast costs big time. Those are REALLY expensive minutes - more than the rental on some airplanes. Real world case; let's use your figures for simplicity's sake: I want to drive from Vancouver to Kelowna. A little check with Google Maps tells us that that's a distance of... ....393 kilometers, or about 245 miles. At 65, that takes me about 3 hours, 45 minutes and I use about 13 gallons of gas. At 55, it takes 4 hours, 30 minutes and I use about 10 gallons of gas. Even at Canadian gas prices, those 10 litres of fuel cost me only about $11.50. Is that really too much to pay to save 45 minutes of my precious time? 25 cents a minute seem pretty cheap to me. Bill Daniels "Morgans" wrote in message ... "Ernest Christley" wrote I've seen SUV's with what looks like reverse scoops that could have to catch the air passing over the top of the vehicle and blow it down the back. Counterintuitive until you realize that attached flow offers less drag. That scoop helps drag, but more importantly, it prevents carbon monoxide from entering in the back window when it is open and driving at highway speeds. When a chopped off SUV has the window open, that low pressure area in the back gathers up the exhaust, and the swirling motion of the vortex allows some to enter in though the open window. Not good. The scoop supplies fresh air flowing down from the top, and keeps the bad air down lower than the open window. They have been doing that since the 60's, on old station wagons, before they cared about mileage and aerodynamics. -- Jim in NC -- Alan Baker Vancouver, British Columbia "If you raise the ceiling four feet, move the fireplace from that wall to that wall, you'll still only get the full stereophonic effect if you sit in the bottom of that cupboard." |
#9
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![]()
Bill Daniels wrote:
You guys haven't mentioned the biggie - roof racks. Removing the cross bars from my Grand Cherokee added 2MPG. Glider pilots look at roof racks and see open air brakes. I can't believe the number of vehicles I see in Denver with ski racks in July. Then, of course, you can park the truck. I understand that trucks have very low drag when parked. If the vehicle has a MPG computer, you can see what speed does to MPG. At 65, my Jeep gets 19MPG. At 55, it gets 24MPG. At 45, it gets 36MPG. If you do the numbers, saving two minutes by driving fast costs big time. Those are REALLY expensive minutes - more than the rental on some airplanes. Bill Daniels Can't argue against the open drag brake idea. I have a nice pair on my Blazer. My impression is that they are there to enhance roll-over protection. I don't have the MPG computer, but I just drove down to Centerville last weekend. 120 miles alnost exactly. V6 4 speed automatic - with highay gearing, it's NOT a tow truck. (and when I hook the boat on the back the Blazer whines and whimpers) 22 MPG going down at 75-85 mph. 26 coming back ar 65. But about 18 around town... Bringing the boat home from Khema - in stop and go Houston traffic - climbing the ovepasses from a standing stop - first 100 miles at 10 to 25 MPH took 10 gallons. After that, at about 50 MPH I got more like 15-16 MPG. (The boat is 18 ft long, but over 1500 pounds - plus a heavy trailer) As they say, YMMV. Sometimes a LOT... Richard |
#10
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![]() "Bill Daniels" bildan@comcast-dot-net wrote in message . .. You guys haven't mentioned the biggie - roof racks. Removing the cross bars from my Grand Cherokee added 2MPG. Glider pilots look at roof racks and see open air brakes. I can't believe the number of vehicles I see in Denver with ski racks in July. Then, of course, you can park the truck. I understand that trucks have very low drag when parked. If the vehicle has a MPG computer, you can see what speed does to MPG. At 65, my Jeep gets 19MPG. At 55, it gets 24MPG. At 45, it gets 36MPG. If you do the numbers, saving two minutes by driving fast costs big time. Those are REALLY expensive minutes - more than the rental on some airplanes. Bill Daniels Those numbers really bother me. The numbers are all fairly low; but the curve shape fits aerodynamic drag, with no other influence such as tires or "pumping losses." In effect, the numbers fit a much larger, but aerodynamically atrocious and very lightly loaded vehicle. Therefore, I really doubt that your mileage computer is telling you the whole truth. Have you 1) verified you odometer against at least 10 miles of highway mile markers, 2) verified your speedometer reading at 60MPH as a result of the same test, and 3) checked the cumulative fuel mileage, as shown on the computer, against your fuel mileage calculated in the usual way? Peter |
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